Exposure apparatus and method which synchronously moves the mask and the substrate to measure displacement

ABSTRACT

There is disclosed an exposure method for transferring, using an optical system for illuminating a mask having patterns to be transferred on a substrate and a projection optical system for projecting images of the patterns to the substrate, the patterns to the substrate through the projection optical system by means of scanning the mask and the substrate synchronously relative to the projection optical system. The method comprises the steps of providing a plurality of measuring marks on the mask formed along a relative scanning direction, and providing a plurality of reference marks formed on the stage corresponding to the measuring marks, respectively, moving the mask and the substrate synchronously in the relative scanning direction to measure successively a displacement amount between the measuring marks on the mask and the reference marks, and obtaining a correspondence relation between a coordinate system on the mask and a coordinate system on the stage according to the displacement amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/831,770 filedApr. 2, 1997, (now U.S. Pat. No. 5,844,247 issued Dec. 4, 1998) and adivision of application Ser. No. 08/608,086 filed Feb. 28, 1996 (nowU.S. Pat. No. 5,646,413 issued Jul. 8, 1997), and a continuation ofapplication Ser. No. 08/476,912 filed Jun. 7, 1995, (abandoned) and acontinuation of application Ser. No. 08/203,037 filed Feb. 28, 1994(abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of exposing and an apparatustherefor. More particularly, the present invention relates to anexposure apparatus of, for example, a slit scanning exposure type and anexposure method advantageously applicable to such apparatus.

2. Related Background Art

Projection type exposure apparatus has been used in manufacturingsemiconductor devices, liquid crystal displays and thin-film magneticheads through a photolithography process, in which patterns of aphotomask or a reticle (hereinafter, referred generally to as "reticle")are transferred to the surface of a substrate (wafer, glass plate, etc.)coated with a photosensitive coating.

The conventional projection type exposure apparatus commonly used is areduction projection type exposure apparatus (stepper) that movesindividual shots on the wafer successively to an exposing field of aprojection optical system to reproduce pattern images of the reticle onthe shots using a photographic step-and-repeat process.

In the typical steppers, a wafer coordinate system is corresponded to areticle coordinate system (reticle alignment).

Some steppers comprise an alignment microscope of an off-axis typeprovided at one side surface of the projection optical system to detecta position of the alignment mark (wafer mark) formed as a correspondenceto each shot on the wafer. In such a case, the shot on the wafer isdetermined within the exposing field of the projection optical systemaccording to the position of the associated wafer mark detected on thealignment microscope. Accordingly, so-called base line amount should beobtained previously that represents a distance between a reference point(such as an exposure center) within the exposing field of the projectionoptical system and a reference point in an observing field of thealignment microscope of the off-axis type.

The reticle alignment and the base line measurement are disclosed indetail in, for example, Japanese Patent Application Laid-Open No.4-324923 (corresponding to U.S. patent application Ser. No. 872,750(filed on Apr. 21, 1992)).

In recent years, fine patterns for the semiconductor devices requireresolution of the projection optical system to be improved. To improvethe resolution, exposing light may be shifted to a shorter wavelength oralternatively, the number of openings of the projection optical systemmay be increased. In any event, it has been difficult to maintain animage quality (such as distortion and image plate deformation) on theentire exposing field with a predetermined accuracy when it is intendedto ensure as same exposing field as conventional arts. With thisrespect, the projection type exposure apparatuses based on so-calledslit scanning exposure type have taken a favorable turn.

In the projection type exposure apparatus of the slit scanning exposuretype, the reticle and the wafer are scanned relative to and synchronouswith a rectangular or arc-shaped illumination field (hereinafter,referred to as a "slit-shaped illumination field") to transfer thepatterns of the reticle on the wafer. The slit scanning exposure typethus makes it possible to reduce the exposing field of the projectionoptical system as compared with the stepper type, provided that thereproduced patterns are equal in area to those reproduced using thestepper type. This may improve the accuracy of the image quality withinthe exposing field. A six-inch size is dominant for the conventionalreticles while a one-fifth factor is dominant as the projectionmagnification of the projection optical system. At the magnification ofone-fifth factor, the six-inch reticle may sometimes be insufficient forrecent circuit patterns of the semiconductor device having the increasedarea. As a result, the projection optical systems should so designedthat the projection magnification of the projection optical system ischanged to, for example, quarter factors. To comply with requirementsfor such reproduced patterns having the increased area, the slitscanning exposure type can advantageously be applied.

In this event, the alignment method based on the reticle and wafercoordinate systems used in the conventional steppers may be unfavorablewhen being applied to the projection type exposure apparatus of the slitscanning type. The projection magnification of quarter factors adverselyaffects the accuracy of the alignment because the alignment becomes moresensitive to writing errors of the circuit patterns on the reticle.

A technique has been suggested in the above mentioned U.S. patentapplication Ser. No. 872,750 (filed on Apr. 21, 1992) to measure arotation angle of the reticle by means of measuring simultaneously theamount of displacement of two or more measuring marks rather than movingthe wafer stages in the wafer. However, the idea of measuring therotation angle using the simultaneous measuring of the measuring markscannot be applied to scanning directions of the projection type exposureapparatus of the slit scanning exposure type. Thus, there is adisadvantage that it is impossible to measure the rotation angle of thereticle and wafer coordinate systems and orthogonal amount of thecoordinates of these coordinate systems.

As for the method of measuring the base line amount between thereference position within the exposing field of the projection opticalsystem and the reference position of the alignment system of theoff-axis type, the conventional measuring method using a pair or markson the reticle in the stepper is disadvantageous, when it is applied tothe projection type exposure apparatus of the slit scanning exposuretype with no modification, in that the writing error of the reticlesignificantly affects the measurements.

SUMMARY OF THE INVENTION

With respect to these problems, the present invention is directed toprovide an exposure method and an exposure apparatus capable of reducingaffect of the writing error between the patterns on the reticle (mask),allowing positive alignment of the reticle coordinate system (maskcoordinate system) and the wafer coordinate system (substrate coordinatesystem) in the exposure apparatus of the slit scanning exposure type.

In light of this, speed of operation may sometimes be considered to bemore important than the accuracy of alignment depending on the process.With this respect, another object of the present invention is to providean exposure method and an exposure apparatus capable of aligning thereticle coordinate system (mask coordinate system) with the wafercoordinate system (substrate coordinate system) at a higher throughput.

Yet another object of the present invention is to provide an exposuremethod and an exposure apparatus capable of reducing affect of thewriting error between the patterns on the reticle (mask), allowingpositive measurement of the base line amount between the reference pointin the exposing field of the projection optical system and the referencepoint of the alignment system in the exposure apparatus of the slitscanning exposure type.

Still another object of the present invention is to provide an exposuremethod and an exposure apparatus in which the alignment between thereticle coordinate system (mask coordinate system) and the wafercoordinate system (substrate coordinate system) as well as the base lineamount are obtained for exposure.

In a case where the base line measurement is performed for everypredetermined number of wafer replacements, speed of operation may beconsidered to be more important than the accuracy of alignment. At thesame time, the reticle coordinate system (mask coordinate system) ispreferably aligned to the wafer coordinate system (substrate coordinatesystem). With this respect, another object of the present invention isto provide an exposure method and an exposure apparatus capable ofaligning the reticle coordinate system (mask coordinate system) to thewafer coordinate system (substrate coordinate system) and of measuringthe base line therefor at a higher throughput for every predeterminednumber of wafer replacements.

It is yet another object of the present invention to provide an exposuremethod and an exposure apparatus using a plurality of measuring reticlemarks to reduce affect of, for example, the writing errors betweenpatterns on the reticle (mask).

It is still another object of the present invention to provide anexposure method and an exposure apparatus capable of aligning thereticle coordinate system (mask coordinate system) to the wafercoordinate system (substrate coordinate system) and of measuring thebase line therefor with a high accuracy in consideration of an errorcomponent to a relative scanning direction of the mask to the wafer.

In an exposure method according to a first aspect of the presentinvention, it is provided with an exposure method of transferring, usingan optical system for illuminating a mask having patterns to betransferred to a substrate and a projection optical system forprojecting images of the patterns to the substrate, the patterns on themask to the substrate on a stage through the projection optical systemby means of scanning the mask and the substrate synchronously relativeto the projection optical system, wherein the method comprises the stepsof: providing a plurality of measuring marks on the mask formed along arelative scanning direction, and providing a plurality of referencemarks formed on the stage corresponding to the measuring marks,respectively; moving the mask and the substrate synchronously in therelative scanning direction to measure successively a displacementamount between the measuring marks on the mask and the reference marks;and obtaining a correspondence relation between a coordinate system onthe mask and a coordinate system on the stage according to thedisplacement amount.

In an exposure method according to a second aspect of the presentinvention, it is provided with an exposure method of transferring, usingan exposure apparatus having an optical system for illuminating a maskhaving patterns to be transferred to a substrate, a mask stage forholding the mask, a substrate stage for holding the substrate, aprojection optical system for projecting images of the patterns to thesubstrate, and an alignment system having its detection center at aposition away from the optical axis of the projection optical system ata predetermined distance, the patterns to the substrate through theprojection optical system by means of scanning the mask and thesubstrate synchronously relative to the projection optical system,wherein the method comprises the steps of providing a plurality ofmeasuring marks formed on the mask along a relative scanning direction;providing first reference marks corresponding to a part of the measuringmarks and second reference marks corresponding to the first referencemarks, respectively, the first and the second reference marks beingformed on the stage, the second reference marks being away from thefirst reference marks at a given distance that is recognized previously;moving the mask to the relative scanning direction with the secondreference marks observed through the alignment system to measuresuccessively a displacement amount between the measuring marks on themask and the first reference marks; and obtaining a distance between areference point within an exposing field of the projection opticalsystem and the detection center according to the displacement amountbetween the measuring marks and the first reference marks, to adisplacement amount of the second reference marks observed through thealignment system, and to the given distance previously recognized.

In an exposure method according to a third aspect of the presentinvention, it is provided with an exposure method of transferring, usingan exposure apparatus having an optical system for illuminating a maskhaving patterns to be transferred to a substrate, a mask stage forholding the mask, a substrate stage for holding the substrate, aprojection optical system for projecting images of the patterns to thesubstrate, and an alignment system having its detection center at aposition away from the optical axis of the projection optical system ata predetermined distance, the patterns to the substrate through theprojection optical system by means of scanning the mask and thesubstrate synchronously relative to the projection optical system,wherein the method comprises the steps of providing a plurality ofmeasuring marks formed on the mask along a relative scanning direction;providing first reference marks corresponding to each of the measuringmarks and second reference marks corresponding to the first referencemarks, respectively, the first and the second reference marks beingformed on the stage, the second reference marks being away from thefirst reference marks at a given distance that is recognized previously;moving the mask and the substrate to a scanning direction to measuresuccessively a displacement amount between the measuring marks on themask and the first reference marks; moving the mask and the substraterelatively to the scanning direction to measure successively adisplacement amount of the second reference marks; and obtaining adistance between a reference point within an exposing field of theprojection optical system and the detection center according to thedisplacement amount between the measuring marks and the first referencemarks, to a displacement amount of the second reference marks observedthrough the alignment system, and to the given distance previouslyrecognized.

In an exposure method according to a fourth aspect of the presentinvention, it is provided with an exposure method of transferring, bymeans of illuminating an illumination area of a predetermined shapeusing an illumination light to scan a mask and a substrate synchronouslyrelative to the illumination area of a predetermined shape, patterns onthe mask within the illumination area of the predetermined shape througha projection optical system to the substrate on a stage, wherein themethod comprises, with a plurality of measuring marks formed on the maskalong a relative scanning direction and reference marks formed on thestage corresponding to the measuring marks, a first step for measuring adisplacement amount between a part of the measuring marks and thereference marks corresponding to the part of the measuring marks,respectively; a second step for moving the mask and the substratesynchronously to the relative scanning direction to measure successivelya displacement amount between the measuring marks on the mask and thereference marks corresponding to the measuring marks; and a third stepfor selecting one of the first and the second steps to obtain acorresponding relation between a coordinate system on the mask and acoordinate system on the stage according to the displacement amountbetween the measuring marks and the reference marks, respectively,obtained at the selected step.

In an exposure method according to a fifth aspect of the presentinvention, it is provided with an exposure method of transferring, usingan exposure apparatus having an optical system for illuminating anillumination area of a predetermined shape using an illumination light,a mask stage for holding a mask provided with patterns to be exposed, asubstrate stage for holding a substrate, a projection optical system forprojecting the patterns on the mask to the substrate, an alignmentsystem having its detection center at a position away from the opticalaxis of the projection optical system at a predetermined position, thepatterns on the mask in the illumination area of the predetermined shapethrough the projection optical system to the substrate by means ofscanning the mask and the substrate synchronously relative to theillumination area of the predetermined shape, wherein the methodcomprises, with a plurality of measuring marks formed on the mask alonga relative scanning direction and a plurality of first reference markscorresponding to the measuring marks and second reference markscorresponding to the first reference marks, the first and the secondreference marks being formed on the stage, the second reference marksbeing away from the first reference mark at a given distance that isrecognized previously, a first step for measuring a displacement amountbetween a part of the measuring marks on the mask-and the firstreference marks corresponding to the part of the measuring marks,respectively, and measuring a displacement amount between the secondreference marks corresponding to the part of the first reference mark; asecond step for moving the mask and the substrate in synchronism withthe scanning direction to measure successively a displacement amountbetween the measuring marks and the first reference marks correspondingto the measuring marks, respectively, and a displacement amount of thesecond reference marks; a third step for selecting one of the first andthe second step; and a fourth step for obtaining a correspondingrelation between a coordinate system on the mask stage and a coordinatesystem on the substrate stage and a distance between a reference pointwithin an exposing field of the projection optical system and thedetection center according to information obtained during the stepselected at the third step and a given distance previously recognized.

In an exposure method according to a sixth aspect of the presentinvention, it is provided with an exposure method of transferring, usingan exposure apparatus having an optical system for illuminating anillumination area of a predetermined shape using an illumination light,a mask stage for holding a mask provided with patterns to be exposed, asubstrate stage for holding a substrate, a projection optical system forprojecting the patterns on the mask to the substrate, an alignmentsystem having its detection center at a position away from the opticalaxis of the projection optical system at a predetermined position, thepatterns on the mask in the illumination area of the predetermined shapethrough the projection optical system to the substrate by means ofscanning the mask and the substrate synchronously relative to theillumination area of the predetermined shape, wherein the methodcomprises, with a plurality of measuring marks formed on the mask alonga relative scanning direction and a plurality of first reference markscorresponding to the measuring marks and second reference markscorresponding to the first reference marks, the first and the secondreference marks being formed on the stage, the second reference marksbeing away from the first reference mark at a given distance that isrecognized previously, for every replacement of predetermined number ofsubstrates, a step for measuring a displacement amount between a part ofthe measuring marks on the mask and the first reference markscorresponding to the part of the measuring marks, respectively, andmeasuring a displacement amount between the second reference markscorresponding to the part of the first reference mark; and a step forobtaining a corresponding relation between a coordinate system on themask and a coordinate system on the stage and a distance between areference point within an exposing field of the projection opticalsystem and the detection center according to a displacement amountbetween one measuring mark and one first reference mark, to adisplacement amount of the second reference marks, and to the givendistance recognized previously.

According to the first exposure method of this invention, it is possibleto reduce affect of the writing error of the measuring marks on the maskby means of obtaining a parameter (such as the magnification, a scalingin the scanning direction, rotation, degree of parallelism in thescanning direction, and offsets in an X direction and a Y direction) foruse in aligning the mask coordinate system with the substrate coordinatesystem by using the least square approximation by means of, finally,matching the displacement obtained, for example, at each position of themeasuring mark on the mark.

According to the second exposure method, it is possible to measurepositively the base line amount or the distance between the referencepoint of the projection optical system and the reference point of thealignment system by means of reducing the writing error of the measuringmarks on the mask through measurement regarding to the measuring markson the mask side.

According to the third exposure method, a plurality-of first referencemarks are formed on a reference mark member with being correspondentwith the measuring marks, respectively, on the mask. In addition, aplurality of second reference marks are formed at such a distance thatcorresponds to the distance between the reference point within theexposing field of the projection optical system and the reference pointof the alignment system from the first reference marks. Accordingly, thebase line amount can be measured more positively because the balancingis made across the reference marks.

According to the fourth exposure method, simple measuring steps based ona quick mode are selected, which allows calculation of the correspondingrelation between the coordinate system on the mask and the coordinatesystem on the stage at a higher throughput depending on the necessities.

According to the fifth exposure method, simple measuring steps based ona quick mode are selected, which allows calculation of the correspondingrelation between the coordinate system on the mask and the coordinatesystem on the stage as well as the base line amount at a higherthroughput depending on the necessities.

According to the sixth exposure method, simple measuring steps based ona quick mode are performed for every exposure of a predetermined numberof substrates, which allows calculation of the corresponding relationbetween the coordinate system on the mask and the coordinate system onthe stage as well as the base line amount at a higher throughput whenmany substrates are subjected to exposure continuously through thescanning method.

In an exposure method according to a seventh aspect of the presentinvention, it is provided with an exposure method for transferring, bymeans of illuminating an illumination area of a predetermined shapeusing an illumination light and scanning a mask and a substratesynchronously relative to the illumination area of the predeterminedshape, patterns on the mask in the illumination area of thepredetermined shape to the substrate on a stage through a projectionoptical system, wherein the method comprises, with a plurality ofmeasuring marks formed on the mask along a relative scanning directionand a plurality of reference marks formed on the stage corresponding toa part of the measuring marks, the steps of moving the mask to therelative scanning direction to measure successively a displacementamount between the measuring marks on the mask and the reference marks;and obtaining a corresponding relation between a coordinate system onthe mask and a coordinate system on the stage.

In an exposure method according to an eighth aspect of the presentinvention, it is provided with an exposure method for transferring,using an exposure apparatus having an optical system for illuminating anillumination area of a predetermined shape using an illumination light,a mask stage for holding a mask provided with patterns to be exposed, asubstrate stage for holding a substrate, a projection optical system forprojecting the patterns on the mask to the substrate, an alignmentsystem having its detection center at a position away from the opticalaxis of the projection optical system at a predetermined position, thepatterns on the mask in the illumination area of the predetermined shapethrough the projection optical system to the substrate by means ofscanning the mask and the substrate synchronously relative to theillumination area of the predetermined shape, wherein the methodcomprises the steps of forming on the substrate stage a reference markdetectable by the alignment system to measure a displacement amount ofthe reference marks by the alignment system; entering a mark error ofthe mask; and obtaining a corresponding relation between a coordinatesystem on the mask stage and a coordinate system on the substrate stage,and a distance between a reference pint within an exposing field of theprojection optical system and the detection center.

In an exposure apparatus according to a first aspect of the presentinvention, it is provided with an exposure apparatus comprising a maskstage for holding a mask provided with patterns to be transferred; asubstrate stage for holding a substrate; an optical system forilluminating the mask using an illumination light; a projection opticalsystem for projecting images of the patterns on the mask to thesubstrate; and a first mark detecting system for detecting a mask markformed at a predetermined position on the mask within an exposing fieldof the projection optical system, the exposure apparatus being for usein scanning the mask and the substrate synchronously relative to theprojection optical system to transfer the patterns on the mask to thesubstrate through the projection optical system, wherein the apparatusfurther comprises a reference plate provided on the substrate stage, thereference plate comprising a plurality of first reference marksdetectable by the first mark detecting system through the projectionoptical system; a plurality of measuring marks provided on the mask,each of the measuring marks being provided along a relative scanningdirection with being correspondent with the reference mark; a drivingcontrol system for use in observing a part of the first reference marksand a part of the measuring marks through the first mark detectingsystem to move the mask stage and the substrate stage to the relativescanning direction such that a displacement amount between the measuringmarks on the mask and the reference marks is measured successively; andcalculating means for calculating a corresponding relation between acoordinate system on the mask stage and a coordinate system on thesubstrate stage.

In an exposure apparatus according to a second aspect of the presentinvention, it is provided with an exposure apparatus comprising a maskstage for holding a mask provided with patterns to be transferred; asubstrate stage for holding a substrate; an optical system forilluminating the mask using an illumination light; a projection opticalsystem for projecting images of the patterns on the mask to thesubstrate; and a first mark detecting system for detecting a mask markformed at a predetermined position on the mask within an exposing fieldof the projection optical system, the apparatus being for use inscanning the mask and the substrate synchronously relative to theprojection optical system to transfer the patterns on the mask to thesubstrate through the projection optical system, wherein the apparatusfurther comprises a reference plate provided on the substrate stage, thereference plate comprising a plurality of first reference marksdetectable by the first mark detecting system through the projectionsystem and second reference marks provided with being away from thefirst reference marks at a given distance that is recognized previously;a plurality of measuring marks provided on the mask, each of themeasuring mask being provided along the relative scanning direction withbeing correspondent with the first reference mark; a driving controlsystem for use in moving the mask stage and the substrate stage to therelative scanning direction such that the part of the measuring marksand the part of the reference marks are observed through the first markdetecting system and a displace amounts are measured successivelybetween the measuring marks on the mask and the reference marks as wellas between the second reference marks with one of a plurality of secondreference marks being observed through a second mark detecting system;and calculating means for calculating a corresponding relation between acoordinate system on the mask stage and a coordinate system on thesubstrate stage and a distance between a reference point within anexposing field of the projection optical system and the detection centeraccording to the displacement amounts measured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram showing a projection type exposureapparatus to which an embodiment of a projection exposure methodaccording to the present invention is applicable;

FIG. 2 is comprised of FIGS. 2A and 2B showing flow charts illustratingan exposure method and a base line amount check method according to afirst embodiment of the present invention;

FIG. 3 is a perspective view showing a reticle loader system;

FIG. 4A is a view for use in describing an arrangement of alignmentmarks on a reticle;

FIG. 4B is a view for use in describing an arrangement of alignmentmarks or the like in an area conjugated with an effective field of aprojection optical system;

FIG. 4C is an enlarged view of fine alignment marks 29A, 29B, 29C, 29D,30A, 30B, 30C and 30D;

FIG. 5A is a view for use in describing how to align a reticle roughly;

FIG. 5B is a view showing a reduced version of FIG. 5A;

FIGS. 6A, 6B, 6C, 6D, 6E and 6F are views showing waveforms of imagepick-up signals supplied from an image pick-up device during a roughalignment of the reticle;

FIG. 7A is a plan view of a stage at a wafer side;

FIG. 7B is a plan view of a stage at a reticle side;

FIG. 8A is a projection view showing arrangement of marks on thereticle;

FIG. 8B is an enlarged projection view showing an example of marks onthe reticle;

FIG. 8C is a plan view showing arrangement of the reference marks on areference mark plate 6;

FIG. 8D is an enlarged view showing an example of a reference mark 35Aor the like;

FIG. 8E is a plan view showing an example of a reference mark 37A or thelike;

FIG. 9 is a plan view for use in describing relation among the referencemark plate, the reticle, the projection optical system and the alignmentdevice during measurement of reticle alignment and a base line amount;

FIG. 10 is a view showing error vectors obtained by means of measuringthe reticle alignment and the base line amount;

FIG. 11 is a partially cutaway structural diagram showing structure of areticle alignment microscope 19 and an illumination system;

FIG. 12A is a view showing an image observed through the image pick-updevice in FIG. 11;

FIGS. 12B and 12C are views showing waveforms indicative of imagesignals in an X direction and a Y direction corresponding to the imageshown in FIG. 12A;

FIG. 13 is a structural diagram showing an alignment device 34 of anoff-axis type;

FIG. 14A is a view showing an image observed through the image pick-updevice in FIG. 13;

FIGS. 14B and 14C are views showing waveforms indicative of imagesignals in an X direction and a Y direction corresponding to the imageshown in FIG. 14A;

FIGS. 14D and 14E are views showing detection signals obtained throughan LIA optical system shown in FIG. 13;

FIG. 15 is comprised of FIGS. 15A and 15B showing flow chartsillustrating a part of operation of an exposure method and a base lineamount check method according to a second embodiment;

FIG. 16 is a flow chart illustrating a remaining part of the operationof the alignment method and the base line amount check method accordingto the second embodiment; and

FIG. 17 is a flow chart illustrating operation of an exposure methodaccording to a third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A projection exposure method according to a first embodiment of thepresent invention is now described with reference to the drawings. Thisembodiment is when the present invention is applied to a case wherepatterns on the reticle are exposed on a wafer by using a projectiontype exposure apparatus of a slit scanning exposure type.

FIG. 1 shows a projection type exposure apparatus according to thisembodiment. In FIG. 1, patterns on a reticle 12 are illuminated throughan illumination area (hereinafter, referred to as a "slit-shapedillumination area") of a rectangular shape formed by an exposing lightEL from an illuminating optical system which is not shown in the figure.Images of the patterns are projected and exposed on a wafer 5 through aprojection optical system 8. In this event, the wafer 5 is scannedbackward from the perspective to the surface of FIG. 1 at a constantvelocity V/M (where 1/M is a reduction magnification of the projectionoptical system 8) in synchronism with the scanning of the reticle 12forward from the perspective of the surface of FIG. 1 at the constantvelocity of V relative to the slit-shaped illumination area of theexposing light EL.

Described is a driving system for the reticle 12 and the wafer 5. Areticle Y-driving stage 10 is mounted on a reticle supporting platform9. The reticle Y-driving stage 10 is drivable in a direction of a Y axis(a direction perpendicular to the paper surface of FIG. 1). A reticlefine driving stage 11 is mounted on the reticle Y-direction drivingstage 10. The reticle 12 is held by a vacuum chuck or the like on thereticle fine driving stage 11. The reticle fine driving stage 11controls a position of the reticle 12 slightly with a high accuracy inan X direction parallel to the paper surface of FIG. 1, Y direction anda rotation direction (θ direction) within a plane orthogonal to theoptical axis of the projection optical system 8. A movable mirror 21 isdisposed on the reticle fine driving stage 11. Positions of the reticlefine driving stage 11 are monitored continuously in the X, Y and θdirections through an interferometer 14 disposed on the reticlesupporting platform 9. Position information S1 obtained by theinterferometer 14 is supplied to a main control system 22A.

A wafer Y-axis driving stage 2 is mounted on a wafer supportingplatform 1. The wafer Y-axis driving stage 2 is drivable in a directionof the Y-axis. A wafer X-axis driving stage 3 is mounted on the waferY-axis driving stage 2. The wafer X-axis driving stage 3 is drivable ina direction of an X-axis. A Zθ-axis driving stage 4 is so disposed onthe wafer X-axis driving state 3 that is drivable in at least therotation direction. The wafer 5 is held on the Zθ-axis driving stage 4by vacuum. A movable mirror 7 is secured to the Zθ-axis driving stage 4.Positions of the Zθ-axis driving stage 4 are monitored in the X, Y and θdirections through an interferometer 13 arranged outside. Positioninformation obtained by the interferometer 13 is also supplied to themain control system 22A. The main control system 22A controlspositioning operation, through a wafer driving device 22B or the like,the wafer Y-axis driving stage 2, the wafer X-axis driving stage 3 andthe Zθ-axis driving stage 4 and controls the operation of the entiredevice.

As will be described later, a reference mark plate 6 is secured to thesurface of the Zθ-axis driving stage 4 at a position close to the wafer5 to align a wafer coordinate system and a reticle coordinate system.The wafer coordinate system is defined by a coordinate measured by theinterferometer 13 at the wafer side. The reticle coordinate system isdefined by a coordinate measured by the interferometer 14 at the reticleside. Various reference marks are formed on the reference mark plate 6as will be described later. Some of these reference marks (luminousreference marks) are illuminated from the backside (from the side of theZθ-axis driving stage 4) by an illumination light led to the Zθ-axisdriving stage 4 side.

Reticle alignment microscopes 19 and 20 are provided over the reticle 12of this embodiment to observe the reference marks on the reference markplate 6 and the marks on the reticle 12 simultaneously. In such a case,deflection mirrors 15 and 16 are movably disposed to lead the detectionlight supplied from the reticle 12 to the reticle alignment microscopes19 and 20, respectively. When an alignment sequence begins, thedeflection mirrors 15 and 16 are withdrawn by mirror driving devices 17and 18 in response to a command supplied from the main control system22A. An alignment device 34 of the off-axis type is also provided at aY-direction side of the projection optical system 8 to observe thealignment marks (wafer marks) on the wafer 5.

A keyboard 22C is connected to the main control system 22A, allowing anoperator to enter commands. The projection aligner according to thisembodiment has a quick mode for measuring quickly the base line amountor the like along with a mode for measuring the same with a highaccuracy as will be described below. An operator indicates that the modeto be executed is whether the high accuracy mode or the quick modethrough the keyboard 22C to the main control system 22A.

Next, described with reference to flow charts in FIGS. 2A and 2B is anoperational sequence from loading to the wafer 5 and reticle 12 tocompletion of the alignment in the projection type exposure apparatusaccording to this embodiment. First, at step 101 in FIG. 2A, reticle 12is subjected to prealignment based on external form reference on areticle loader (described below).

FIG. 3 shows a reticle loader system for use in carrying the reticle 12to the reticle fine driving stage 11 shown in FIG. 1. The reticle loaderin FIG. 3 comprises two reticle arms 23A and 23B, an arm rotation axis25 connected to the reticle arms 23A and 23B, and a rotation mechanism26 for rotating the arm rotation axis 25. Grooves 24A and 24B forvacuuming are formed in a reticle mounting surface of the reticle arms23A and 23B, respectively. The reticle arms 23A and 23B are so supportedthat they can rotate independently of each other through the armrotation axis 25.

During loading of the reticle 12, the reticle 12 is passed to thereticle arm 23A through a reticle carrying mechanism (not shown) at aposition A3. At that time, the other reticle arm 23B is used forcarrying, for example, another reticle used during a previous process. Areticle configuration prealignment mechanism (not shown) mounted nearthe position A3 aligns the reticle 12 on the reticle arm 23A based onthe external form thereof with a predetermined accuracy. Subsequently,the reticle 12 is subjected to vacuum suction to the reticle arm 23A.Next, at step 102 in FIG. 2A, the rotation mechanism 26 rotates thereticle arm 23A through the arm rotation axis 25 to move the reticle 12to a position B3 in the Y direction (a ready position (passing position)of the reticle driving stage 10 in FIG. 1).

In this event, the groove 24A for vacuum suction is a groove extendingin a direction orthogonal to a suction position (parallel direction ofthe groove 24A) on the reticle fine driving stage 11 and is located outof a pattern area of the reticle 12. Accordingly, the reticle arm 23A isallowed to advance and retract the reticle 12 freely to and from thereticle fine driving stage 11 with the reticle fine driving stage 11moved to the topmost in the y direction or the scanning direction. Whenthe reticle 12 arrives over the reticle fine driving stage 11 (FIG. 1),the arm rotation axis 25 retracts in a -Z direction. The reticle 12 isthus mounted on the vacuum suction surface of the reticle fine drivingstage 11. After completion of passing of the reticle 12, the reticle arm23A is withdrawn. Subsequently, the reticle fine driving stage 11carries the reticle 12 towards a position C3. In this event, the reticlearms 23A and 23B are driven independently of each other. The reticlepassing speed is increased by means of simultaneously performing loadingand unloading of the reticles by these arms.

Next, at steps following step 103 the reticle 12 is aligned. A mechanismand operation therefor are described.

FIG. 4A shows arrangement of alignment marks (reticle marks) on thereticle 12. FIG. 4B shows a slit-shaped illumination area 32 or the likewithin an area 33R conjugated with an effective exposing field of theprojection optical system over the reticle. A y direction corresponds toa scanning direction while an x direction corresponds to a directionorthogonal to the y direction. In FIG. 4A, a shield portion 31 is formedalong a periphery of a pattern area at the center of the reticle 12.Reticle marks formed outside the shield portion 31 are: rough searchingalignment marks 27 and 28 and fine alignment marks 29A, 29B, 29C, 29D,30A, 30B, 30C and 30D. The rough searching alignment mark 27 at theright-hand side is formed of an elongated linear pattern and crosspatterns. The linear pattern extends along the y direction or thescanning direction and the cross patterns are formed at both ends of thelinear pattern. The searching alignment mark 28 at the left-hand side isformed symmetrically with the rough searching alignment mark 27 at theright-hand side.

The fine alignment marks 29A and 29B are provided near the y directionbetween the shield portion 31 at the right-hand side and one crosspattern of the rough searching alignment mark 27. The fine alignmentmarks 29C and 29D are provided near the y direction between the shieldportion 31 at the right-hand side and the other cross pattern of therough searching alignment mark 27. The fine alignment marks 30A, 30B,30C and 30D are formed at the left-hand side symmetrically with the finealignment marks 29A, 29B, 29C and 29D, respectively. While each of thefine alignment marks 29A, 29B, 29C, 29D, 30A, 30B, 30C and 30D is shownas a cross mark in FIG. 4A, it is formed of two sets of three linearpatterns arranged in the x direction at a predetermined distance and twosets of three linear patterns arranged in the y direction at apredetermined distance as shown in FIG. 4C. At step 103 in FIG. 2A, therough searching alignment mark 28 at the left-hand side in FIG. 4A isdetected by the reticle alignment microscope (hereinafter referred to as"RA microscope") 20. FIG. 4B shows observation areas 19R and 20R of theRA microscopes 19 and 20, respectively, on the reticle 12. During roughsearching, the rough searching alignment marks 27 and 28 are located outof the observation areas 19R and 20R and also out of an area 33Rconjugated with the effective exposing field. This is because the roughsearching alignment marks 27 and 28 should be large enough for roughsearching but the exposing field of the projection optical system is notso large, otherwise the diameter of a projection lens should beincreased, resulting in increase of the costs. With this respect,procedures for performing the rough search in this embodiment isdescribed in conjunction with FIGS. 5A and 5B.

FIG. 5A is an enlarged view of one cross pattern and its periphery ofthe rough searching alignment mark 28. FIG. 5B is a reduced version ofFIG. 5A. In FIGS. 5A and 5B, W represents a width of a square effectivefield of view 20Ref of the RA microscope 20 and ΔR represents a designedvalue of a sum of a writing error and a mounting error of the patternsrelative to the outer configuration of the reticle 12. Accordingly, asshown in FIG. 5B, one cross pattern 28a of the rough searching alignmentmark 28 is always contained within a square area having the width of ΔR.What are to be detected are x and y coordinates of the cross pattern28a. In this embodiment, the effective field of view 20R_(ef) having thewidth of W is scanned diagonally to the x and y axes in a directionpassing at 45° to two axes of the alignment mark 28. The x and ycoordinates of the cross pattern 28a are obtained as the x and ycoordinates at that time when the alignment mark 28 is diagonallyscanned.

For this purpose, an integer portion of a positive real number isrepresented by INTA. The number of search fields or the least number ofscanning of the square area having the width ΔR with the effective fieldof view 20R_(ef) having the width W can be given by {INTA (ΔR/W)+1}.This number of search fields is previously obtained. The {INTA (ΔR/W)+1}effective fields of view A5, B5, C5, . . . , each having the width W areset diagonally to the square area having the width ΔR around the firsteffective field of view B5. The reticle fine driving stage 11 shown inFIG. 1 is driven to step the effective fields of view, thereby samplingimages within each effective field of view while setting themsuccessively within the effective field of view 20R_(ef) in FIG. 5A.

As shown in FIG. 5B, the cross pattern 28a of the alignment mark 28 tobe searched is present within a search boundary having the width andlength of at least ΔR×ΔR. The alignment mark 28 is large enough to thesearch boundary. Accordingly, to step the effective fields of view in adiagonal direction to the alignment mark 28 makes it possible to detectthe coordinates of the cross pattern 28a of the alignment mark 28 with aleast number of fields. The image processing at that time may be aone-dimensional image processing on image signals obtained by means ofadding the scanning lines of all lines within the picked-up image.

FIGS. 6A to 6F show image signals obtained by means of so adding thescanning lines of all lines. FIGS. 6A and 6D represent image signalsobtained along the x and y directions, respectively, within theeffective field of view A5 in FIG. 5B. FIGS. 6B and 6E represent imagesignals obtained along the x and y directions, respectively, within theeffective field of view B5 in FIG. 5B. FIGS. 6C and 6F represent imagesignals obtained along the x and y directions, respectively, within theeffective field of view C5 in FIG. 5B. The x coordinate of the crosspattern 28a is obtained from the image signal shown in FIG. 6B while they coordinate thereof is obtained from the image signal shown in FIG. 6F.

After detecting the searching reticle mark 28 in this manner, the roughsearching alignment mark 27 is moved to the observation area of the RAmicroscope 19 at step 104 in FIG. 2A. The position of the alignment mark27 is detected in the same manner as described above. In this event, theportion of the reference mark plate 6 where no pattern is included ismoved within the exposing field of the projection optical system 8 toilluminate the portion from the bottom. The illumination light emittedfrom the reference mark plate 6 allows illumination of the roughsearching alignment marks 27 and 28 from the backside (zθ-axis drivingstage side).

The above mentioned sequence roughly aligns the position of the roughsearching alignment marks 27 and 28 and the reticle coordinate systemrelative to the observation areas 19R and 20R of the RA microscopes 19and 20 in FIG. 4B. In addition, rough alignment of the observation areas19R and 20R of the RA microscopes with the wafer coordinate system canbe made by means of measuring the reference marks on the reference markplate 6 in FIG. 1 through the RA microscopes 19 and 20. As a result,rough alignment is completed such that the fine alignment marks 29A,29B, 29C, 29D, 30A, 30B, 30C and 30D are not overlapped with thereference marks (described below) of the reference mark plate 6.

In this embodiment, the alignment marks on the reticle 12 are formed ofthe rough searching alignment marks and the fine alignment marks for thepurpose of reducing the diameter of the lens of the projection opticalsystem 8. However, the rough searching alignment marks may be used asthe fine alignment marks when a lens of the larger diameter can beavailable. In such a case, searching can be made in the same manner onthe alignment marks by means of stepping in a diagonal direction asshown in FIGS. 5A and 5B. The searching of the alignment marks can bemade simultaneously through the RA microscopes 19 and 20.

Next, a sequence for fine alignment is described. Detailed structure ofthe wafer stage and the reticle stage is described first.

FIG. 7A is a plan view of the wafer stage. In FIG. 7A, the wafer 5 andthe reference mark plate 6 are disposed on the Zθ-axis driving stage 4.Movable mirrors 7X and 7Y for the X and Y axes, respectively, aresecured to the Zθ-axis driving stage 4. A slit-shaped illumination area32W, corresponding to the slit-shaped illumination area 32 in FIG. 4B,is illuminated by an exposing light on the wafer 5. Observation areas19W and 20W are conjugated with the observation area 19R and 20R,respectively, in FIG. 4B.

Laser beams LWX and LW_(of) are directed to the movable mirror 7X at adistance IL in the direction parallel to the X axis along optical pathspassing the optical axis of the projection optical system and areference point of the alignment device 34, respectively. Laser beamsLWY1 and LWY2 are directed to the movable mirror 7Y along optical pathsparallel to the Y axis. During alignment and exposure, a coordinatevalue measured by an interferometer using the laser beam LWX is used asthe X coordinate of the Zθ-axis driving stage 4. Used as the Ycoordinate is an average (Y₁ +Y₂)/2 of coordinate values Y₁ and Y2measured by interferometers using the laser beams LWY1 and LWY2,respectively. For example, the rotation amount in the rotation direction(θ direction) of the Zθ-axis driving stage 4 can be measured accordingto the difference between the coordinate values Y₁ and Y₂. The positionand a rotation amount within an XY plane of the Zθ-axis driving stage 4is controlled according to these coordinates.

In particular, for the Y direction or the scanning direction, an errordue to air fluctuation or the like during scanning is relieved using anaveraging effect by means of applying the average value of the measuredresults obtained by two interferometers. When the alignment device 34 ofthe off-axis type is used, the position in the X-axis direction is socontrolled as not to cause a so-called Abbe's error according tomeasured values of an exclusive interferometer using the laser beamLW_(of).

FIG. 7B is a plan view of the reticle stage. In FIG. 7B, the reticlefine driving stage 11 is mounted on the reticle Y-axis driving stage 10,on which the reticle 12 is held. A movable mirror 21x for the x axis andtwo movable mirrors 21y1 and 21y2 for the y axis are secured to thereticle fine driving stage 11. A laser beam LRx is directed to themovable mirror 21x in parallel with the x axis. Laser beams LRy1 andLRy2 are directed to the movable mirrors 21y and 21y2, respectively, inparallel with the y axis.

As in the case of the wafer stage, a coordinate in the y direction ofthe reticle fine driving stage 11 is an average value of (y₁ +y₂)/2 ofcoordinates y₁ and y₂ measured by two interferometers using the laserbeams LRy1 and LRy2, respectively. A coordinate in the x direction is acoordinate value measured by an interferometer using the laser beam LRx.The rotation amount in a direction (θ direction) of the reticle finedriving stage 11 is measured according to the difference between, forexample, the coordinate values y₁ and y₂.

In this event, corner-cube reflector elements are used as the movablemirrors 21y1 and 21y2 in the y direction or the scanning direction. Thelaser beams LRy1 and LRy2 reflected from the movable mirrors 21y1 and21y2 are in turn reflected back from reflection mirrors 39 and 38,respectively. More specifically, the interferometer for the reticle is adouble-path interferometer. Accordingly, rotation of the reticle finedriving stage 11 does not shift or displace the position of the laserbeams. As in the case of the wafer stage, the reticle 12 is providedwith the slit-shaped illumination area 32 and the observation areas 19Rand 20R of the RA microscopes 19 and 20, respectively. The Zθ-axisdriving stage 4 in FIG. 7A and the reticle 12 can be observed onlythrough the observation areas 19R and 20R. A relation between thereticle 12 and the Zθ-axis driving stage 4 is so measured as to improvethe rotation accuracy of the reticle 12 and the wafer 5 as well as thealignment accuracy on exposing. A method thereof is described inconjunction with FIGS. 8A, 8B, 8C, 8D, 8E and 9.

FIG. 8A shows an reticle image 12W obtained by means of projecting thereticle 12 to the reference mark plate 6 in FIG. 7A. In FIG. 8A, shownare mark images 29AW, 29BW, 29CW and 29DW conjugated with the finealignment marks 29A, 29B, 29C and 29D, respectively, in FIG. 4A and markimages 30AW, 30BW, 30CW and 30DW conjugated with the fine alignmentmarks 30A, 30B, 30C and 30D, respectively. Each of the mark images 29AW,29BW, 29CW, 29DW, 30AW, 30BW, 30CW and 30DW is formed of four sides eachcomprising three linear patterns as shown in FIG. 8B.

FIG. 8C shows arrangement of reference marks on the reference mark plate6. Formed on the reference mark plate 6 in FIG. 8C are reference marks35A, 35B, 35C, 35D, 36A, 36B, 36C and 36D arranged in a manner similarto the mark images 29AW, 29BW, 29CW, 29DW, 30AW, 30BW, 30CW and 30DW inFIG. 8A. These reference marks are illuminated by an illumination lightthat is equal in wavelength to the exposing light. A reference mark 37Ais also provided on the reference mark plate 6 at a position away from acenter between the reference marks 35A and 36A at a distance IL in the Ydirection or the scanning direction. The distance IL corresponds to thebase line amount, the distance between the reference point of theprojection optical system 8 in FIG. 1 and the reference point of thealignment device 34 of the off-axis type. Likewise, reference marks 37B,37C and 37D are formed as positions away from centers between thereference marks 35B and 36B, between the reference marks 35C and 36C,and between the reference marks 35D and 36D, respectively, at a distanceIL in the Y direction.

Each of the reference marks 35A, 35B, 35C, 35D, 36A, 36B, 36C and 36D isformed of linear patterns of 7-row by 7-column as shown in FIG. 8D. Thereference marks 35A, 35B, 35C, 35D, 36A, 36B, 36C, and 36D have sizessmaller than the mark images 29AW, 29BW, 29CW, 29DW, 30AW, 30BW, 30CWand 30DW in FIG. 8B. The reference marks 37A, 37B, 37C and 37D are, asshown in FIG. 8E, associated lattice points of a grid pattern formed ata predetermined pitch in the X and Y directions.

In such a case, at step 105 in FIG. 2A, a relative position relation anda relative rotation angle of the reticle 12 and the RA microscopes 19and 20 are calculated on the basis of the results obtained at the steps103 and 104 to move the fine alignment marks 29A and 30A in FIG. 4A intothe-observation area 19R and 20R of the RA microscopes 19 and 20,respectively. Subsequently, at step 106, the reference marks 35A and 36Aon the reference mark plate 6 in FIG. 8C are moved into the observationareas 19W and 20W (see FIG. 9) conjugated with the observation areas 19Rand 20R, respectively. As a result, the mark image 29AW and thereference mark 35A are observed simultaneously within the observationarea 19W and the mark image 30AW and the reference mark 36A are observedsimultaneously within the observation area 20W as shown in a portiondepicted by 220 in FIG. 9. Subsequently, at step 107 in FIG. 2A, theimages observed through the RA microscopes 19 and 20 are converted intoimage pick-up signals and sampled. At the same time, the detectionsignals of the associated reference mark images are also sampled in thealignment device 34 of the off-axis type.

At the portion 220 in FIG. 9, the reticle image 12W or the projectionimage of the reticle is projected to the reference mark plate 6. Asshown in a portion 222 in FIG. 9, the observation areas 19W and 20W arelocated at positions passing the optical axis within the exposing fieldof the projection optical system 8. The reference mark 37A is within theobservation area of the alignment device 34 of the off-axis type. As inthe case of the slit scanning exposure, the reticle fine driving stage11 in FIG. 7B is moved downward (to a -y direction) in synchronism withmovement of the Zθ-axis driving stage 4 in FIG. 7A upward (to the Ydirection). As a result, the reference mark plate 6 and the reticleimage 12W are moved together to the Y direction as shown in 220 and 221in FIG. 9. In this event, the observation areas 19W and 20W of the RAmicroscopes 19 and 20 and the alignment device 34 of the off-axis typeare all fixed, so that from a set of marks with a symbol A (the markimages 29AW, 30AW, the reference marks 35A, 36A and 37A) to a set ofmarks with a symbol D (the mark images 29DW, 30DW, the reference marks35D, 36D and 37D) are moved under the observation areas 19W and 20W andthe alignment device 34.

At a first stop position after initiation of alignment shown in theportion 220 in FIG. 9, the mark image 29AW and the reference mark 35Aare located under the observation area 19W. The mark image 30A and thereference mark 36A are located under the observation area 20W. Thereference mark 37A is located under the alignment device 34 of theoff-axis type. These marks with the symbol A are all observed at thesame time. After completion of measurement at the first stop position,the reticle image 12W and the reference mark plate 6 are movedsynchronously to a second stop position by the stepping operation. Theset of marks observed at the first stop position under the observationareas 19W and 20W and the alignment device 34 is a set of marks with thesymbol A while the set of marks present at this second stop positionunder the observation areas 19W and 20W and the alignment device 34 is aset of marks with a symbol B (the mark image 29BW in FIG. 8A, thereference marks 35B, 37B in FIG. 8C or the like).

By means of repeating the above mentioned sequence for third and fourthstop positions (as shown in 221 in FIG. 9), the mark image of thereticle image 12W and the reference marks on the reference mark plate 6are measured through the RA microscopes 19 and 20 and the alignmentdevice 34 of the off-axis type in the order of the set of marks with thesymbol A, the set of marks with the symbol B, the set of marks with thesymbol C and the set of marks with the symbol D. This corresponds-to theoperation illustrated in the steps 105 through 110 in FIGS. 2A and 2B.The so obtained measured result is clearly shown in FIG. 10.

In FIG. 10, a vector of the alignment error of the reference mark 35Athrough the mark image 29AW is referred to as AL that is obtained bymeans of correcting the measured result obtained through the RAmicroscope 19 in the following manner. Likewise, vectors of thealignment errors of the reference marks 35B, 35C and 35D through themark image 29BW, 29CW and 29DW are referred to as BL, CL and DL,respectively. Likewise, ΔR represents a vector of the alignment error ofthe reference mark 36A through the mark image 30AW. BR, CR and DRrepresent vectors of the alignment errors of the reference marks 36B,36C and 36D through the mark image 30BW, 30CW and 30DW, respectively. Inaddition, an error vector from the reference marks 37A, 37B, 37C and 37Dto the reference point of the alignment device 34 are referred to as AO,BO, CO and DO, respectively, that are obtained by means of correctingthe measured result obtained through the alignment device 34 of theoff-axis type in a manner described below.

ReAx, ReBx, ReCx and ReDx represent the coordinate values in the xdirection measured by the interferometer 14 at the reticle side in FIG.1, i.e., the coordinate values obtained by using the laser beam LRx inFIG. 7B when the error vectors AL, AR, BL, BR, CL, CR, DL and DR areobtained. ReAy1, ReBy1, ReCy1, ReDy1, ReAy2, ReBy2, ReCy2 and ReDy2represent the coordinate values in the y direction measured by theinterferometer 14 at the reticle side in FIG. 1, i.e., the coordinatevalues obtained by using the laser beams LRy1 and LRy2 in FIG. 7B whenthe error vectors AL, AR, BL, BR, CL, CR, DL and DR are obtained. WeAx,WaBx, WaCx and WaDx represent the coordinate values in the X directionmeasured by the interferometer 13 at the wafer side in FIG. 1, i.e., thecoordinate values obtained by using the laser beam LWX in FIG. 7A whenthe error vectors AL, AR, BL, BR, CL, CR, DL and DR are obtained. WaAY1,WaBY1, WaCY1, WaDY1, WaAY2, WaBY2, WaCY2 and WaDY2 represent thecoordinate values in the Y direction measured by the interferometer 13at the reticle side in FIG. 1, i.e., the coordinate values obtained byusing the laser beams LWY1 and LWY2 in FIG. 7A when the error vectorsAL, AR, BL, BR, CL, CR, DL and DR are obtained.

WaAOX, WaBOX, WaCOX and WaDOX represent the coordinate values in the Xdirection measured by the interferometer exclusive for the alignmentdevice of the off-axis type at the wafer side in FIG. 1, i.e., thecoordinate values obtained by using the laser beam LW_(OF) in FIG. 7Awhen the error vectors AO, BO, CO and DO. In this event, as shown inFIG. 7A, the distance between the laser beams LWY1 and LWY2 at the waferside in the X direction is IL and the distance at the wafer side betweenthe laser beams LRy1 and LRy2 at the reticle side is RL.

Next, structure of the RA microscope 19 in FIG. 1 is described in detailfor use in describing how to obtain the error vector AL or the like.

FIG. 11 shows the RA microscope 19 and its illumination system. In FIG.11, an illumination light EL having the same wavelength as the exposinglight is introduced into the Zθ-axis driving stage 4 from the outside ofthe Zθ-axis driving stage 4 through an optical fiber 44. An exposinglight may be relayed through lens systems rather than using the opticalfiber 44. The so introduced illumination light illuminates the referencemarks 35A, 35B, 35C and 35D on the reference mark plate 6 through a lens45A, a beam splitter 45B and a lens 45C. The illumination lighttransmitted through the beam splitter 45B illuminates the referencemarks 36A, 36B, 36C and 36D on the reference mark plate 6 through a lens45D, a lens 45E, a mirror 45F and a lens 45G.

For example, the light transmitted through the reference mark 35Afocuses an image of the reference mark 35A on the file alignment mark29A on the reticle 12. The light from the image of the reference mark35A and the alignment mark 29A is reached to a half mirror 42 through adeflection mirror 15, a lens 40A and a lens 40B. The light divided intotwo portions through the half mirror 42 are directed to image pick-upsurfaces of image pick-up devices 43X and 43Y, respectively, for the Xand Y axes, each of which being formed of two dimensionalcharged-coupled-device (CCD). The image 35AR of the reference mark 35Aand the fine alignment mark 29A as shown in FIG. 12A are projected onthe image pick-up devices 43Y and 43X, respectively. In this event, animage pick-up field 43Xa of the image pick-up device 43 for the X axisis an area parallel to the X direction of the wafer stage and thedirection of the horizontal scanning lines also corresponds to the Xdirection. An image pick-up field 43Ya of the image pick-up device 43Yfor the Y axis is an area parallel to the Y direction of the wafer stageand the direction of the horizontal scanning line corresponds to the Ydirection.

Accordingly, a displacement amount in the x direction between thereference mark 35A and the alignment mark 29A can be obtained accordingto an averaging of image pick-up signals S4X obtained by the imagepick-up device 43X. A displacement amount in the Y direction between thereference mark 35A and the alignment mark 29A can be obtained accordingto an averaging of image pick-up signals S4Y obtained by the imagepick-up device 43Y. These image pick-up signals S4X and S4Y are suppliedto a signal processing device 41 (see FIG. 11).

More specifically, description is made in conjunction with anexemplified case where the set of marks with the symbol A issubjected-to alignment. For example, the alignment mark 29A and thereference mark 35AR shown in FIG. 12A are observed through the RAmicroscope 19 at the same time. In FIG. 12A, the image signals S4X andS4Y within the image pick-up fields 43Xa and 43Ya enclosed by brokenlines are detected as digital signals by means of carrying out ananalog-to-digital conversion in the signal processing device 41. Theimage data on the individual scanning lines are averaged independentlyfor the X and Y axes in the signal processing device 41. The averagedimage signals S4X' and S4Y' for the X and Y axes, respectively, are asshown in FIGS. 12B and 12C, respectively. These image data are processedas one-dimensional image processing signals.

Calculation and processing on the so obtained signals in the signalprocessing device 41 produces relative displacements AL'_(X) and AL'_(Y)in the X and Y directions between the mark image 29AW of the reticle 12and the reference mark 35A of the reference mark plate 6 in FIG. 10.Using the RA microscope 20 in FIG. 1, obtained are relativedisplacements AR'_(X) and AR'_(Y) in the X and Y directions between themark image 30AW and the reference mark 36A. Likewise, obtained arerelative displacements between the mark images 29BW, 29CW and 29DW andthe reference marks 35B, 35C and 35D, respectively, in FIG. 10 andrelative displacements between the mark images 30BW, 30CW and 30DW andthe reference marks 36B, 36C and 36D, respectively.

However, the image signal corresponding to the alignment mark 29A andthe image signal corresponding to the reference mark image 35AR in FIG.12B are controlled in position by the interferometer at the reticle sideand the interferometer at the wafer side, respectively. Accordingly,measurement errors (=measured value-set value), ΔReAx, ΔReAy1, ΔReAy2,ΔWaAX, ΔWaAY1, and ΔWaAY2 are caused due to following errors at theindividual stages with respect to the measured coordinates ReAx, ReAy1and ReAy2 obtained by the interferometer at the reticle side and themeasured coordinates WaAX, WaAY1 and WaAY2 obtained by theinterferometer at the wafer side during measurement of the set of markswith the symbol A (29AW, 35A, 30AW and 36A in FIG. 10). Thesemeasurement errors are contained in the relative displacements AL'_(X)and AL'_(Y) obtained through the calculation.

With this respect, the results obtained by means of subtracting theerrors from the relative displacements obtained through measurementcorrespond to an X component AL_(X) and a Y component AL_(Y) of thevector of the alignment error in FIG. 10. In this event, (1/M) in afollowing equation represents a reduction magnification of theprojection optical system 8, while IL and RL represent the distancesdescribed in conjunction with FIG. 7A.

    AL.sub.X =AL'.sub.X -ΔReAx/M-ΔWaAX             (Equation 1),

and ##EQU1##

Likewise, an X component AR_(X) and a component AR_(Y) of the vector ARof the alignment error in FIG. 10 can be given by following equations.

    AR.sub.X =AR'.sub.X -AReAx/M-ΔWaAX                   (Equation 3),

and ##EQU2##

Next, structure of the alignment device 34 is described in conjunctionwith FIG. 13 for use in describing the error vectors AO, BO, CO and DOin FIG. 10 obtained by means-of correcting the results obtained by thealignment device 34 of the off-axis type.

FIG. 13 shows structure of the alignment device 34. In FIG. 13, thelight from the reference mark on the reference mark plate 6 is deflectedfrom a deflection mirror unit 46 and is directed to a half prism 47. Thelight reflected from the half prism 47 is directed to an alignmentoptical system 48 (hereinafter, referred to as "FIA optical system") ofan image processing type using white light. The light transmittedthrough the half mirror is directed to an alignment optical system 52(hereinafter, referred to as "LIA optical system") for use in detectingthe diffraction light from lattice marks using a heterodyne beam.

Describing about the FIA optical system 48, the illumination light froman illumination light source 49 is passed through the FIA optical system48 and is deflected through the half prism 47 and the deflection mirror46 to illuminate the reference marks on the reference mark plate 6. Theback light therefrom goes back to the FIA optical system through thesame optical path. The light transmitted through the FIA optical systemis directed to a half prism 50A. The light beam transmitted through thehalf prism 50A focuses an image of the reference mark of the referencemark plate 6 on the image pick-up surface of an image pick-up device 51Xfor the X axis formed of a two-dimensional CCD. The light beam reflectedfrom the half prism 50A focuses an image of the reference mark of thereference mark plate 6 on the image pick-up surface of an image pick-updevice 51Y for the Y axis formed of a two-dimensional CCD.

On the image pick-up surfaces of the image pick-up devices 51X and 51Y,images shown in FIG. 14A are focused. The reference marks on thereference mark plate 6 are grating points of the grating pattern. FIG.14A shows an image 37P of the grating pattern. It is assumed that P andL represent grating pitch on the reference mark plate 6 of the image 37Pof the grating pattern and a width of a dark line, respectively, thewidth L is significantly smaller than the pitch P. Focused on the imagepick-up surface are reference mark (index mark) images 48X1 and 48X2 inthe X direction and index mark images 48Y1 and 48Y2 in the Y directionilluminated by another illumination light other than the illuminationlight for the reference mark plate 6. The position of the referencemarks on the reference mark plate 6 can be detected with the position ofthe index marks as the reference.

More specifically, image pick-up area 51Xa and 51Ya in the directionsconjugated with the X and Y directions, respectively, in FIG. 14A arepicked up through the image pick-up devices 51X and 51Y in FIG. 13. Thedirections of the horizontal scanning lines of the image pick-up devices51X and 51Y are directions conjugated with the X and Y directions,respectively. Image pick-up signals S5X and S5Y obtained by the imagepick-up devices 51X and 51Y, respectively, are supplied to a signalprocessing device 56 in FIG. 13. The signal processing device 56averages the image pick-up signals S5X and S5Y to produce image signalsS5X' and S5Y' shown in FIGS. 14B and 14C, respectively. A displacementof the directed reference mark on the reference mark plate 6 is obtainedaccording to these image signals. More detailed structure is disclosedin Japanese Patent Application No. 4-16589.

It is assumed that relative displacements in the X and Y directions ofthe reference mark 37A relative to the reference mark obtained as aresult of the image processing in FIG. 14A are represented by AO'_(fX)and AO'_(fY) when the reference mark to be detected is the referencemark 37A in FIG. 10. In this event, the position of the reference markplate 6 is controlled on the wafer coordinate system, so that valuesobtained by subtracting the follow error and the rotation error of theZθ-axis driving stage 4 in FIG. 7A from the measured result are an Xcomponent AO_(X) and a Y component AO_(Y) of the error vector AO in FIG.10. The X component AO_(X) and the Y component AO_(Y) corresponding tothe FIA optical system 48 in FIG. 13 are represented by AOf_(X) andAO_(fY). That is, following equations are given:

    AO.sub.fX =AO'.sub.fX -(WaAOX-WaAX)                        (Equation 5),

and

    AO.sub.fY =AO'.sub.fY -(WaAY1+WaAY2)/2                     (Equation 6).

On the other hand, in the alignment system containing the LIA opticalsystem 52 in FIG. 13, a laser beam emitted from a laser beam source 53is transmitted through the LIA optical system 52 and the half prism 47,which is then deflected from the deflection mirror 46 and directed tothe reference mark of a diffraction grating shape on the reference markplate 6. The diffracted light from the reference mark goes back to theLIA optical system 52 through the same optical path. The diffractedlight transmitted through the LIA optical system 52 is divided into twoportions through a half prism 50B and directed to photosensitiveelements 55X and 55Y for the X and Y directions, respectively.

In this event, the laser beam emitted from the laser beam source 53 inthe LIA optical system 52 is divided into two portions. A frequencydifference of Δf is caused between frequencies of these two laser beamsby an internal frequency shifter. Interference light of these two laserbeams is received by a photosensitive element 54. The photosensitiveelement 54 produces a reference signal S6 having a frequency of Δf. Twolaser beams having different frequencies (heterodyne beams) are directedto the reference mark of the diffraction grating shape on the referencemark plate 6 at an adequate incident angle. A ±1 order diffracted lightof these two laser beams from the reference mark returns in parallel inan orthogonal manner relative to the reference mark plate 6. Aninterference light of the ±1 order light has an intensity varied at thefrequency Δf and a phase thereof varies depending on the X and Ycoordinates of the reference mark. The photosensitive element 55Xproduces a beat signal S7X having the frequency Δf and a phase varieddepending on the X coordinate of the reference mark. The photosensitiveelement 55Y produces a beat signal S7Y having the frequency Δf and aphase varied depending on the Y coordinate of the reference mark. Thereference signal S6 and the beat signals S7X and S7Y are supplied to thesignal processing device 56.

The signal processing device 56 in FIG. 13 calculates a displacementAO'Lx in the X direction of the reference mark 37A according to a phasedifference Δφ_(X) between the reference signal S6 and the beat signalS7X as shown in FIG. 14D and calculates a displacement AO'_(LX) in the Ydirection of the reference mark 37A according to a phase differenceΔφ_(Y) between the reference signal S6 and the beat signal S7X as shownin FIG. 14E when the reference mark to be detected is the reference mark37A in FIG. 10. When the following error and the rotation error of theZθ-axis driving stage 4 in FIG. 7A are subtracted from the abovecalculation result, the X component AO_(X) and Y component AO_(Y) of theerror vector in FIG. 10 can be obtained. Let the X and Y componentsAO_(X) and AO_(Y) of the LIA optical system 52 in FIG. 13 be AO_(LX) andAO_(LY), respectively. That is, the following equation can be given:

    AO.sub.LX =AO'.sub.LX -(WaAOX-WaAX)                        (Equation 7),

and

    AO.sub.LY =AO'.sub.LY -(WaAY1+WaAY2)/2                     (Equation 8).

In the above mentioned manner, eight data AL_(X), AL_(Y), AR_(X),AR_(Y), AO_(fX), AO_(fY), AO_(LX) and AO_(LY) are measured by means ofperforming alignment at the positions of the mark group with the symbolA in FIG. 10. Measurement on the mark groups with the symbols A throughD in such a sequence produces thirty-two (=8×4) data. Of thesethirty-two data, the data obtained through the RA microscopes 19 and 20are stored as measured data D_(xn), D_(yn) while the data obtainedthrough the alignment device 34 of the off-axis type is stored asmeasured data A_(xn), A_(yn). Subsequently, the operation proceeds tostep 111 in FIG. 2B. At the step 111 in FIG. 2B, it is assumed thatcoordinates in the x and y directions are F_(xn) and F_(yn) on acoordinate system where the reticle coordinate system and the wafercoordinate system are adapted to convert with only the linear error withrespect to the measured data D_(xn), D_(yn) corresponding to the RAmicroscopes 19 and 20. The following relation holds: ##EQU3##

In addition, let nonlinear errors in the x and y directions be ε_(xn)and ε_(yn), respectively, then the following equation can be given:##EQU4##

Six parameters in Equation 9, Rx, Ry, θ, ω, Ox and Oy, are calculated byusing the least square approximation to minimize the nonlinear error(ε_(xn), ε_(yn)). In this event, the scaling parameter Rx in the xdirection indicates a magnification error in the x direction between thereticle 12 and the reference mark plate 6. The scaling parameter Ryindicates a scaling error in the scanning direction (y direction)between the reticle coordinate system and the wafer coordinate system.The angle parameter θ represents the rotation error between the reticle12 and the reference mark plate 6. The angle parameter ω represents theparallelism in the scanning direction of the reticle coordinate systemand the wafer coordinate system. The offset parameters Ox and Oyrepresent offset values in the x and y directions, respectively.

Next, at steps 112 and 113 in FIG. 2B, the base line amount is obtained.Let averages of the data A_(xn) and A_(yn) measured through thealignment device 34 of the off-axis type be <Ax> and <Ay>, respectively,then the offset during measurement of the base line amount becomes(<Ax>-Ox, <Ay>-Oy). Accordingly, control should be switched duringalignment from the interferometer using the laser beam LWX in FIG. 7A(hereinafter, also refereed to as "exposing interferometer LWX") to theinterferometer using the laser beam LW_(OF) (hereinafter, also referredto as "off-axis exclusive interferometer LW_(Of) "). When the FIAoptical system 48 in FIG. 13 is used, averages of the measured dataA_(xn) and A_(yn) are represented by <Afx>and <Afy>, respectively. Then,the offset of the offset (<Afx>-Ox, <Afy>-Oy) is taken intoconsideration in the measured values of the interferometer correspondingto the laser beams LWY1, LWY2 and LW_(OF) to perform the alignment. Onthe other hand, when the LIA optical system 52 in FIG. 13 is used,averages of the measured data A_(xn) and A_(yn) are represented by <ALx>and <ALy>, respectively. Then, the offset (<ALx>-Ox, <ALy>-Oy) is takeninto consideration in the measured values of the interferometer.

According to the above, the base line amount obtained corresponds towhat the base line amount (distance IL) is corrected with the offset of(<Afx>-Ox, <Afy>-Oy) or the offset of (<ALx>-Ox, <ALy>-Oy).

The above mentioned correction technique means that the referencecoordinate system of the stage coordinate system is set according to thereference marks on the reference mark plate 6. In such a case, in otherwords, an axis passing the reference marks 37A, 37B, 37C and 37D on thereference mark plate 6 serves as a reference axis, and obtained is aread value (yawing value) of the off-axis exclusive interferometerLW_(OF) on this reference axis with the read value of the exposinginterferometer LWX of zero on this reference axis. During exposure, byusing, as "values of the interferometers for delivery", the read valueof the exposing interferometer LWX and the result of yawing valuecorrection made on the read value (yawing value) of the off-axisexclusive interferometer LW_(OF), the positioning of the wafer 5 isperformed according to these values for the delivery.

On the other hand, in FIG. 7A for example, an alternative method may beused where the movable mirror 7X for the X axis is used as the referenceaxis of the stage coordinate system. In such a case, in a conditionshown in FIG. 7A, the read values of the exposing interferometer LWX andthe off-axis exclusive interferometer LWoF are reset simultaneously (tozero), the measured values are used for the subsequent exposure withoutusing the interferometer values for delivery. On the other hand, duringalignment, obtained is an inclined angle θ_(XF) of the reference axispassing the reference marks 37A, 37B, 37C and 37D on the reference markplate 6 relative to the movable mirror 7X. Then, such a value is usedthat is obtained by means of correcting with IL·θ_(XF) on the read valueof the off-axis exclusive interferometer LW_(OF) using the distance ILbetween the laser beams LWX and LW_(OF). As a result, it becomespossible to use the read values of the exposing interferometer LWX andthe off-axis exclusive interferometer LWOF as they are during exposure.

Next, the measured data D_(xn), D_(yn) represents only the relativeerror between the wafer coordinate system and the reticle coordinatesystem. Accordingly, when the least square approximation is performedusing the wafer coordinate system as a reference, the obtainedparameters RX, Ry, θ, ω, Ox and Oy are all represented as the linearerrors of the reticle coordinate system with the wafer coordinate systemas the reference. With this respect, let the x and y coordinates of thereticle coordinate system be r_(xn) ' and r_(yn) ', respectively, thereticle may be driven according to a fresh coordinates (r_(xn) ', r_(yn)') obtained, depending on the movement of the wafer coordinate system,by the following equation: ##EQU5##

In this processing, the offsets Ox and Oy has already been corrected atthe reticle side, so that only the offset of (<Ax>, <Ay>) is required tobe corrected as the base line amount. In addition, when the reticlecoordinate system is used as the reference, the results are all reversedand correction may be made on the wafer coordinate system. Thesecorrections may be controlled separately by means of correcting on thewafer coordinate system during the rough alignment and correcting on thereticle coordinate system during the fine alignment.

As mentioned above, according to the present invention, the reticlealignment and check of the base line amount are made during a singlealignment using a plurality of marks, so that it becomes possible toaverage the writing error of the reticle and the positioning errorbetween the reticle and the wafer. This improves the accuracy ofalignment. In addition, these processes are simultaneously performed inparallel, improving the throughput of the operation. Further, there isno error due to the air fluctuation of the optical path of theinterferometers because the reference mark plate 6 is applied that iscapable of measuring the reference marks at the same time in thenon-scanning direction (X direction).

However, the reference mark plate 6 moves stepwise in the scanningdirection and there may be an effect of the air fluctuation. With thisrespect, the position of the wafer stage (Zθ-axis driving stage 4 or thelike) is locked to check the reticle alignment and the base line amountby using the output values of the photosensitive devices 55X and 55Y inprocessing with the LIA optical system 52 in FIG. 13 for checking thebase line amount. This minimizes the effect of the air fluctuation. Inaddition, the reticle marks in this embodiment are arranged at eightpositions on the four corners of the reticle 12. This is because theparameters Rx, Ry, θ and ω are necessary as well as the offsets to checkthe relation between the reticle coordinate system and the wafercoordinate system and thus it is more advantageous to determine theparameters Ry, θ and ω with the marks arranged at four corners. Further,that is because, when the reference mark plate 6 used is a lightemitting type, it is difficult to emit light from entire surface on thereference mark plate 6 due to limitation on a light emitting portion.

In addition, let the number of the reticle marks on the reticle 12 be n,then the offset parameters OX and OY are averaged into 1/n^(1/2), anderrors in the other parameters become small. Accordingly, the more thenumber n of the reticle marks, the smaller the error is. A simulationresult on the relation among the number n of the reticle marks, theerror in the parameters and the error in the base line amount is setforth below. In the following, distribution at four corners on the freshcoordinate system of (Equation 11) is represented as three times aslarge as a standard deviation σ with a unit of [nm].

                  TABLE 1                                                         ______________________________________                                        Number n of                                                                   Reticle marks                                                                                  Error in                                                                                          Error in Base                                                                  Worse                                   Axis of                RX, Ry, θ, ω                                                          Line Amount                                                                                Square                                Coordinates X      Y         X    Y      Sum                                  ______________________________________                                         4          9.59   10.96     8.8  7.2    16.00                                 8                    7.92   7.10                                                                                  5.1     9.43                             12                    6.48  5.86                                                                                   4.2     7.77                             16                    5.80  5.03                                                                                   3.6     6.83                             ______________________________________                                    

It is revealed from the above that the number n of the reticle marksbeing equal to eight makes it possible to ensure the check accuracy onthe base line amount and the reticle alignment of 10 nm or less evenwhen the reticle writing error is 50 nm and the stepping error of thestage is 10 nm. In other words, the higher accuracy may be achieved bymeans of increasing the number n of the reticle marks with theprocessing speed increased within the limitation of the reference markplate 6 of the light emitting type.

In such a case, a patterning error on the reference mark plate 6 and adistortion error of the projection optical system 8 are left as theerrors in the fresh coordinate system. However, there is no trouble atall when exposure results are compared with reference data in adjustingthe device and the results obtained are eliminated as system offsetsbecause these errors are hardly fluctuated.

In the above mentioned embodiment, on the reference mark plate 6provided are a plurality of reference marks 35A, 35B, 35C and 35D and aplurality of reference marks 37A, 37B, 37C and 37D as shown in FIG. 8C.However, the corresponding relation between the reticle coordinatesystem and the wafer coordinate system may be obtained by means of, forexample, scanning only the reticle 12 by using a single reference mark35A and a single reference mark 37A, thereby averaging or least squareapproximating the measured results. This approach also contributes toreduce the effect of the writing error of the patterns on the reticle12.

Next, a second embodiment of the present invention is described inconjunction with flow charts illustrated in FIGS. 15A, 15B and 16. Asfor this, the reticle alignment mode in the above mentioned firstembodiment is based on the fine alignment using four pairs of finealignment marks 29A, 29B, 29C, 29D, 30A, 30B, 30C and 30D on thereticle.

However, a single pair of fine alignment marks may be used for thereticle alignment or the base line measurement after the reticlealignment is once performed finely by means of the method described inthe first embodiment if the scaling error in the scanning direction orthe parallelism between the reticle coordinate system and the wafercoordinate system are small. Such an alignment mode for measuring onthree items: measuring a magnification (Rx) in the non-scanningdirection, measuring rotation (θ) and measuring the base line using thesingle pair of alignment mark is referred to as a quick mode. In thisquick mode, it is necessary to store the writing error between the marks29A and 30A obtained in the fine alignment sequence to correct thewriting error between the fine alignment marks 29A and 30A.

Operation of this second embodiment is described with reference to FIGS.15A, 15B and 16. Operation in FIGS. 15A, 15B and 16 is the operation ofFIGS. 2A and 2B with the addition of the quick mode, in which switchingbetween the fine mode and the quick mode can be available. At steps inFIGS. 15A and 15B, steps corresponding to those in FIGS. 2A and 2B areindicated by like reference numerals, and detailed description thereofwill be omitted.

In FIGS. 15A and 15B, at steps 101 through 104, the reticle 12 ismounted on the reticle holder and positions of the rough searchingalignment marks 27 and 28 are detected through the RA microscopes 19 and20, respectively, as in the case of FIGS. 2A and 2B. Subsequently,either one of the fine mode or the quick mode is selected at step 115.The selected result is previously indicated by an operator through thekeyboard 22C in FIG. 1. It is noted that pattern information or the likeon the reticle 12 may be read by using a bar-code reader or the likewhich is not shown, according to which the main control system 22A mayautomatically select the alignment mode.

When the fine mode is selected, steps 105 through 113 are executed andthe base line measurement is performed as described above by usingmeasured result on the reticle alignment and the fine alignment using aplurality of fine alignment marks and a plurality of reference marks. Atstep 114, obtained is the writing error (hereinafter, referred to as"mark error") between the positions of the actual fine alignment marks29A and 30A relative to the target positions on the fresh coordinatesystem on the reticle. The mark error is memorized in a memorizing unitin the main control system 22A. In calculating the mark error, thereticle coordinate system is obtained with the wafer coordinate systemused as the reference according to the relation (conversion parameters)obtained at step 113. On this reticle coordinate system, the nonlinearerror is obtained on the measured coordinate values relative to thecoordinate values in design on the fine alignment marks 29A, 29B, 29C,29D, 30A, 30B, 30C and 30D. This nonlinear error corresponds to the markerror. In this way, the mark error on the fresh coordinate system on thereticle is memorized according to the results obtained at steps 112 and113. In addition, if the reticle writing error is previously measured,an operator may enter the writing error directly. When the writing errorcomprises a linear component, this becomes more advantageous.

On the other hand, if the quick mode is selected at the step 115,operation proceeds to step 116 in FIG. 16. At steps 116 through 118, thesame operation is executed as in the steps 105 through 107 in FIG. 1.More specifically, images of a pair of fine alignment marks 30A and 29Aon the reticle and a pair of reference marks 36A and 35A are observedthrough the RA microscopes to detect a single reference mark 37A byusing the alignment device 34 of the off-axis type. In addition, atlater half of step 119, the positions of the marks observed through theRA microscope and the mark detected by the alignment device 34 of theoff-axis type are obtained. Subsequently, at step 119, the mark errorobtained at step 114 in FIG. 15B is corrected relative to the positiondetected on the fine alignment marks 30A and 29A on the reticle 12. As aresult, the-writing error of the patterns on the reticle 12 can becorrected or compensated to the similar degree to the case of the finealignment mode in the first embodiment even if the number of the marksmeasured in the quick mode is small.

Next, at step 120, the magnification error Rx in the non-scanningdirection, the rotation 0 and the offsets Ox, OY are obtained of sixconversion parameters (Rx, Ry, θ, ω, Ox, Oy) in Equation 9 according tothe position of each mark obtained as a result of correction at the step119. More specifically, as shown in FIGS. 8A and 8C, the magnificationerror Rx in the non-scanning direction is obtained from the differencebetween the distance between the marks in the X direction (non-scanningdirection) of the measured reference marks 35A and 36A and the distancebetween the mark images 29A and 30A in the X direction. In addition, therotation θ is obtained from a difference between a displacement betweenthe reference marks 35A and 36A in the Y direction (scanning direction)and a displacement between the mark images 29A and 30A in the Ydirection and the mark distance. The offsets Ox, OY can be givenaccording to a mean displacement between the mark images of thereference mark and the reticle mark.

In the quick mode, the number of marks to be measured is two by each atthe reticle side and the reference mark plate 6 side, so that only fourout of six conversion parameters in Equation 9 are determined. The fourconversion parameters are thus obtained as mentioned above. A scalingerror Ry in the scanning direction may be obtained by means ofselecting, as the marks to be measured, two fine alignment marks 29A and29D aligned in the Y direction in FIGS. 4A to 4C and two reference marks35A and 35D in FIG. 8C.

The reticle alignment is performed according to the magnification errorRx in the non-scanning direction, the rotation θ and the offsets Ox andOy obtained at the step 120. The measurement of the magnification errorRx may be made by means of preparing as a table the magnification errorRx corresponding to the difference in the measured values on the marksfrom the designed values, thereby the magnification error Rx may beobtained with the difference between the measured values on the marksand the designed values on the marks being applied to the table.

Next, at step 121, the base line measurement is performed by using themeasured values on the central coordinate of the reference marks 35A and36A as well as the measured value on the reference mark 37A.

In this way, according to this embodiment, when the fine alignment modeis once performed to obtain the writing error (mark error) on thepatterns of the reticle 12 and then the alignment is performed at thequick mode, the error is corrected, so that the alignment of theprojection type exposure apparatus of the slit scanning type can be madeat a high throughput and with a high accuracy.

Next, a third embodiment of the present invention is described inconjunction with a flow chart illustrated in FIG. 17. This thirdembodiment is a case where the reticle alignment and the base linemeasurement are performed in the above mentioned quick mode for everyone replacement of a predetermined number of wafers, i.e., for everyexposure of the predetermined number of wafers. In this embodiment,described with reference to FIG. 17 is an exemplified operation in acase where the reticle is exchanged in the projection type exposureapparatus in FIG. 1, following which the patterns of the reticle 12 aresuccessively exposed on the wafers of which number is equal to, forexample, 100.

First, at step 211 in FIG. 17, the previously used reticle is replacedby the reticle 12 in FIG. 1 for starting the exposing operation. In sucha case, the reticle alignment and base line check operations areperformed in the quick mode that are similar to those illustrated atsteps 101 through 104 and 115 in FIG. 15A and steps 116 through 121 inFIG. 16. Thereafter, the number of wafers to be exposed until the nextreticle alignment and the base line check is set as an initial value ofa variable N at step 212. At step 213, the wafer is loaded on the waferstage 4. When there is any wafer already exposed at step 213, theexposed wafer is first unloaded and then a new wafer is loaded.

Subsequently, at step 214, it is determined whether the variable N isequal to zero, i.e., whether the reticle alignment and the base-linecheck should be performed at that timing. If the variable N is largerthan zero, one is subtracted from the variable N at step 215 to proceedto step 216. At the step 216, the wafer is aligned by using thealignment device 34 of the off-axis type shown in FIG. 13 or thealignment system of the TTL type, following which the patterns of thereticle 12 are exposed on each shot of the wafer. ΔAfter completion ofexposure of all (designated number of) wafers, the exposing process onthat reticle 12 is ended. If there are one or more wafers leftunexposed, the step 213 is again executed to unload the exposed waferand load a new wafer. This step is followed by the step 214.

If the variable N is equal to zero, i.e., whether the reticle alignmentand the base line check should be performed at that timing at the step214, the rotation error and the magnification error of the reticle 12are measured at step 217. This corresponds to the step 120 in FIG. 16.Subsequently, step 218 is carried out to perform the base line check inthe X and Y directions of the alignment device 34 of the off-axis type(the alignment system comprising the FIA optical system 48 or the waferalignment system of a two-beam interference alignment type comprisingthe LIA optical system 52). Thereafter, the number of the wafers to beexposed until the next base line check is set as the variable N at step219, which returns the operation to the step 216.

As mentioned above, according to this invention, the reticle alignmentand the base line measurement are performed for every replacement of thereticle, and the reticle alignment and the base line measurement areperformed in the quick mode for every exposure of the predeterminednumber of wafers. Accordingly, it is possible to increase an overlayaccuracy between the images of the wafer and the reticle at a highthroughput.

While the technique in the above mentioned embodiment has thus beendescribed in conjunction with the base line measurement with thealignment device of the off-axis type used, equivalent effects can beobtained by applying the present invention to a TTL (through the lens)type using within the field of the projection optical system.

It should be understood that the present invention is not limited to theparticular embodiment shown and described above, and various changes andmodifications may be made without departing from the spirit and scope ofthe appended claims.

What is claimed is:
 1. A scanning exposure method in which an objectsupported by a member and an exposure beam are moved relatively in afirst direction during a scanning exposure, the methodcomprising:detecting positional information in the first direction ofthe supporting member using a corner cube type reflection member whichis formed on the supporting member and which is used with a firstinterferometer device; and detecting positional information in a seconddirection perpendicular to the first direction of the supporting memberusing a reflection surface which is substantially parallel to the firstdirection on the supporting member and which is used with a secondinterferometer device.
 2. A scanning exposure method according to claim1, wherein the object includes a mask having a pattern.
 3. A scanningexposure method according to claim 1, wherein said exposure beamincludes light.
 4. A scanning exposure method according to claim 1,further comprising:controlling a position of said supporting memberbased on the detected positional information in said first and seconddirections.
 5. A device which is produced by using a scanning exposuremethod according to claim
 1. 6. A method of making a scanning exposureapparatus in which an object and an exposure beam are moved relativelyin a first direction during a scanning exposure, the methodcomprising:providing a supporting member which is movable in the firstdirection while supporting the object; providing a corner cube typereflection member which is arranged on the supporting member; providinga first interferometer device, optically connected with the corner cubereflection member, which detects positional information in the firstdirection of the supporting member; providing a reflection surface, onthe supporting member, which is substantially parallel to the firstdirection; and providing a second interferometer device, opticallyconnected with the reflection surface, which detects positionalinformation in a second direction perpendicular to the first direction.7. A method according to claim 6, wherein the object includes a maskhaving a pattern.
 8. A method according to claim 6, wherein saidexposure beam includes light.
 9. A method according to claim 6, furthercomprising:providing a controlling system, connected with the first andsecond interferometer devices, which controls a position of thesupporting member based on the positional information detected by thefirst and second interferometer devices.
 10. A method according to claim6, wherein a plurality of the corner cube type reflection members arespaced by a predetermined distance in said second direction and disposedon said supporting member, and said first interferometer device obtainspositional information of said supporting member in said first directionfrom each of said plurality of corner cube type reflection members. 11.A method according to claim 10, further comprising:obtaining rotationalinformation of said supporting member based on said positionalinformation of said supporting member in said first direction obtainedfrom each of said plurality of corner cube type reflection members. 12.A method according to claim 6, wherein said supporting member has afirst driving mechanism for moving said object in said first directionand a second driving mechanism for fine moving said object in said firstdirection, in said second direction, and in a rotational direction. 13.A method according to claim 12, wherein said first driving mechanism hasa first stage movable in said first direction, and said second drivingmechanism has a second stage fine movable in said first direction, insaid second direction and in a rotational direction.
 14. A device whichis produced by a scanning exposure apparatus made by using a methodaccording to claim
 6. 15. A scanning exposure apparatus in which anobject and an exposure beam are moved relatively in a first directionduring a scanning exposure, the apparatus comprising:a supporting memberwhich is movable in the first direction while supporting the object; acorner cube type reflection member which is arranged on the supportingmember; a first interferometer device, optically connected with thecorner cube reflection member, which detects positional information inthe first direction of the supporting member; a reflection surface,provided on the supporting member, which is substantially parallel tothe first direction; and a second interferometer device, opticallyconnected with the reflection surface, which detects positionalinformation in a second direction perpendicular to the first direction.16. A scanning exposure apparatus according to claim 15, wherein theobject includes a mask having a pattern.
 17. A scanning exposureapparatus according to claim 15, wherein said exposure beam includeslight.
 18. A scanning exposure apparatus according to claim 15, whereina plurality of the corner cube type reflection members are spaced by apredetermined distance in said second direction and disposed on saidsupporting member, andsaid interferometer device obtains positionalinformation of said supporting member in said first direction from eachof said plurality of corner cube type reflection members.
 19. A scanningexposure apparatus according to claim 18, wherein rotational informationof said supporting member is obtained based on said positionalinformation of said supporting member in said first direction obtainedfrom each of said plurality of corner cube type reflection members. 20.A scanning exposure apparatus according to claim 15, furthercomprising:a controlling system, connected with the first and secondinterferometer devices, which controls a position of the supportingmember based on the positional information detected by the first andsecond interferometer devices.
 21. A scanning exposure apparatusaccording to claim 20, wherein said supporting member has a firstdriving mechanism for moving said object in said first direction and asecond driving mechanism for fine moving said object in said firstdirection, in said second direction and in a rotational direction.
 22. Ascanning exposure apparatus according to claim 21, wherein said firstdriving mechanism has a first stage movable in said first direction, andsaid second driving mechanism has a second stage fine movable in saidfirst direction, in said second direction and in a rotational direction.